Production of plastics derived from renewable resources is expected to grow to 3.45 million tons by the year 2020, representing a current annual growth rate of approximately 37% for biobased plastics (Plastics Engineering, February 2010, p 16-19). The drivers for growth of biobased plastics include the contribution to global warming from production of petroleum-based plastics, the need to reduce our dependence on limited supplies of petroleum oil, the fluctuating petroleum oil prices as well as environmental disposal problems of common petroleum-based plastics. One objective for manufacturing biobased plastics is to replace as much “fossil” or petroleum-derived carbon with “renewable” carbon in the material as possible. Another objective of biodegradable or compostable bioplastics is to provide alternative end of life options and to develop new applications where degradation provides new performance attributes such as for compostable bags used to transfer food waste to composting or anaerobic digestion facilities or biodegradable mulch films, plastic articles for shoreline restoration, plastic articles for oil or gas production and the like. This invention is generally in the area of biodegradable biobased plastics and we use the term biodegradable and compostable interchangeably. The percentage of “renewable” carbon can be qualitatively measured in polymer materials using 14C radio carbon dating (ASTM D6866 test method). In an ideal situation the biodegradable bioplastics are fully biobased or have a high, say greater than 50% biobased carbon content, preferably greater than 60%, 70%, 80% up to greater than 98% biobased content. This provides additional marketing advantages of interest to consumers who prefer that biodegradable plastics are based as much as possible on renewable resources. The percentage of “renewable” carbon can be qualitatively measured in polymer materials using 14C radio carbon dating (ASTM D6866 test method).
Current examples of biobased biodegradable plastics produced from renewable resources include polylactic acid (PLA) made from lactic acid produced by fermentation of sugar (Nature Works Ingeo™ PLA), polyhydroxyalkanoates (PHA's) produced by the fermentation of glucose (U.S. Pat. Nos. 6,593,116 and 6,913,911 as well as US Patent Pub. No. 2010/0168481) and thermoplastic starch derived from plants such as potato, corn and tapioca.
To optimize the performance properties of biodegradable plastics it is advantageous to blend biobased plastics together. Mechanical properties such as tensile strength, puncture resistance, elongation; thermal properties such as heat distortion temperature and optical properties such as clarity are all important for packaging film applications and therefore require biobased polymers that are both tough and readily processable.
PLA is the most advanced biobased biodegradable plastic in the industry in terms of market penetration and is used in numerous applications including thermoforming, injection molding and coatings. The use of PLA in film applications had been severely limited by the extremely poor physical properties of the films produced to date which are brittle and have very poor strength, tear or puncture resistance. For example the level of PLA that can be blended into the synthetic biodegradable polymer ECOFLEX® produced by BASF is limited to around 15% of the total weight of PLA that can be used due to impairment of film properties. It is one embodiment of the current invention to provide compositions and methods for producing PLA films, in which PLA is the majority component by weight of the biodegradable polymer in the film, usually greater than 65% and PHA is a minority component. Quite unexpectedly these films have been found to have exceptionally good film properties as compared to any other PLA dominated film composition reported to date.
Polyhydroxyalkanoates are unique materials to use as components in biobased biodegradable plastic blends because they are easily blended with many other biodegradable plastics, they can be manufactured as 100% biobased materials and they biodegradable in a number of different environments (water, soil, compost). Genetically-modified biomass systems have recently been developed which produce a wide variety of biodegradable PHA polymers and copolymers with material properties ranging from very hard and brittle to rubber-like elasticity (Lee (1996), Biotechnology & Bioengineering 49:1-14; Braunegg et al. (1998), J. Biotechnology 65:127-161; Madison, L. L. and Huisman, G. W. (1999), Metabolic Engineering of Poly-3-Hydroxyalkanoates; From DNA to Plastic, in: Microbiol. Mol. Biol. Rev. 63:21-53).
Blends of PHA's with other biodegradable plastics have been investigated previously such as blends of PLA with poly-3-hydroxybutrate (P3HB), poly-3-hydroxybutyrate-co-hydroxyvalerate (PHBV) (J. S. Yoon, W. S. Lee, K. S. Kim, I. J. Chin, M. N. Kim and C. Kim, European Polymer Journal, 36, 435 (2000); B. M. P. Ferreira, C. A. C. Zavaglia and E. A. R. Duek, Journal of Applied Polymer Science, 86, 2898 (2002)), poly-3-hydroxybutyrate-co-3-hydroxyhexanoate (P3HB-3HH) (I. Noda, M. M. Satkowski, A. E. Dowrey and C. Marcott, Macromolecular Bioscience, 4, 269 (2004)) and poly-3-hydroxybutyrate-4-hydroxybutyrate (P3HB-co-4HB) ternary blends (International Pub. No. WO2011/146484); blends of PBS and PBSA with P3HB-co-4HB (International Pub. WO2010/151798); blends of P3HB-co-4HB with polybutylene-adipate-terephthalate (PBAT) (US Pub. No 2011/0189414) and blends of P3HB-co-4HB with polyvinyl acetate (PVAc) (International Pub. No 2011/031558). Producing PHA copolymers industrially with the desirable properties for producing PLA blends suitable for producing robust products remains an unmet need in the industry. While the above blends showed basic mechanical properties and a range of biodegradation rates, the biobased content of these blends was not 100% and film products made using these blends had inadequate physical properties for film applications which require good tear strength, puncture resistance and toughness
Therefore, a need exists for producing biobased plastic blends with improved material properties that are biodegradable and have increased, up to 100% biobased content.